Understanding Crochet Thread Sizes

Thread crochet is, for the most part, just like yarn crochet. However, the small differences between the two can make thread crochet a little bit confusing to the crafter who has always worked with yarn. Thread size and hook size are one of the key differences that must be understood to master the art of thread crochet.

Once you understand this part, the rest is all in the details. So, let’s dig in to get a better understanding of the way that crochet thread sizes are numbered and the right crochet hook sizes to go with them.

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Guide to Crochet Thread Sizes

Each type of thread or yarn is assigned a number. With yarn, the higher the number, the thicker the yarn. For example, a DK weight yarn is a 3 and a Bulky Weight yarn is a 5; naturally the larger yarn (in number) is the thicker yarn (in weight). This makes sense to us. However, the opposite is true when it comes to crochet thread.

With thread, the higher the number of the thread, the thinner it is. A size 3 in crochet thread sounds small and a size 30 sounds much larger, but actually a size 3 is going to be a thicker thread than a size 30. As the number of the thread goes up, the thickness goes down.

This can trick the mind a bit, but once you get the hang of it you’ll be okay. One of the best ways to remember this is to make yourself a little chart by taping a small piece of each thread size side-by-side on a piece of paper and labeling each underneath with the size; hang this in your craft space for a visual reminder!

Common Crochet Thread Sizes

You may find crochet thread in a variety of different sizes, particularly if you purchase vintage thread or thread from a foreign source. That said, there are some standard crochet thread sizes.

Size 3 and 5 crochet thread is about as thick as a lightweight yarn, with size 3 being slightly thicker than size 5 (remember, smaller number, thicker thread). If you have trouble learning thread crochet, start with these large sizes of thread.

Size 10 crochet thread is slightly thinner than most yarn, slightly thicker than size 3 or 5 threads. Beginners to thread crochet often find that this is a good size to start with.

Size 20 and 30 crochet thread are common options. Many of the thread crochet patterns that you will find are going to call for one of these two sizes of thread.

People interested in working with even thinner thread will find that it comes in increments of 10 (size 40 to size 100), with the lower numbers being slightly thicker (but still very thin) compared to the highest numbers.

Choosing the Right Crochet Hook for Thread

When working in thread crochet, it is most common to use steel crochet hooks (which are sometimes called “thread hooks”). However, if you are working with the thickest crochet thread (size 3 or 5) then you might instead choose to use a small size of an aluminum or other crochet hook. Those are the crochet hooks that you are already familiar with from working in yarn, the ones given letters for sizes. C, D, and E are all good choices for working with thick crochet thread. Try using a size D crochet hook with a size 3 thread; adjust up or down as needed.

Now, let’s talk about steel crochet hooks.

These hooks have numbers, and you may be surprised to learn that the higher the number, the smaller the hook! This is the opposite of the lettering system for yarn hooks, right? With those crochet hooks, a D is smaller than an E which is smaller than an F and so on. But with thread hooks, a 9 is larger than a 10, not smaller.

This, again, can be a bit confusing at first but most steel crochet hooks are also marked with a mm size, which will make it clear which hook is smaller. For example, a size 9 hook is typically 1.25 mm while a size 10 is 1.15 mm; you can see that the 10 is smaller than the 9. So, when choosing a crochet hook for your thread, you want to choose higher numbers (meaning smaller hooks) for higher thread sizes (which are thinner).

The crochet hook size and thread size match each other in this way.

Okay, so now that you understand that, what are the right size hooks for your thread? Note: This information is for U.S. size crochet hooks. Matching a hook size to a thread size can vary according to the brand of hook and the gauge of the individual crocheter. For this reason, this list can be considered to be approximate but can still be a helpful starting point and will often work out just right. That said, here’s a good starting point:

Size 10 thread works well with a crochet hook sized 7 or 8

Size 20 thread works well with a crochet hook sized 9 or 10

Size 30 thread works well with a crochet hook sized 10, 11 or 12

Size 40 thread works well with a crochet hook sized 11, 12 or 13

Size 60 thread works well with a crochet hook sized 12 or 13

Sized 80 thread works well with a crochet hook sized 13 or 14

Sized 100 thread works well with a crochet hook sized 14

If you are working from a thread crochet pattern, you can start with the hook recommended by the designer, but adjust as needed to get the right gauge. Now you have the knowledge that you need to change the hook / thread size if necessary!